Among the most distasteful of necessary household tasks is cleaning ovens. When foods are roasted or baked in a oven, various amounts of fat, vegetable products, etc., splatter on the top and sides and run down to the bottom of the oven. The heat of the oven surfaces then dehydrates the substances and causes them to polymerize and undergo other chemical changes which produce highly insoluble products which adhere tightly to the oven surfaces and are extremely difficult to remove. In addition, roasting pans, grills, utensils and the like acquire similar coatings. For many years, alkaline paste cleaners were used as chemical agents for cleaning ovens. These cleaners contained large concentrations of lye, which saponifies the fats to soluble soaps and thus facilitates their removal. However, such paste cleaners had to be laboriously painted on to the oven surfaces and the task of removal was just as laborious. Furthermore, since they contained high concentrations of caustic alkalies, in the range of about 8%, rubber gloves had to be worn and, during removal, either large amounts of water had to be used or the alkali had to be neutralized with acidic substances such as vinegar. For household use, such alkali paste cleaners have now been replaced with combinations of alkalies and various solvents, generally packaged in the form of aerosols or sprays. Although the task of cleaning ovens with these substances is considerably less arduous than with paste cleaners, the active ingredient in many of these aerosol or spray cleaners continues to be potassium hydroxide or sodium hydroxide. These caustic alkali compositions provide excellent oven cleaning effectiveness, but there are several drawbacks in their use. Caustic alkalies are dangerous to the eyes and, when used in the form of pressurized aerosol, there is extremely great hazard. Additionally, caustic alkalies are irritating to the skin, thus requiring that the user wear rubber gloves or other protective materials.
In place of caustic alkali compositions, a number of oven cleaning compositions have been developed which contain various other cleaners, solvents, surfactants, builders, etc., all intended to provide oven cleaning effectiveness without the hazards and unpleasantness of caustic alkalies. Most of these non-caustic compositions require that the oven be cleaned at elevated temperatures, generally above 120.degree. C., although there are so-called low temperature oven cleaners which can be used in the 95.degree. C. range with some even claiming to be effective at temperatures as low as about 65.degree. C. Furthermore, even though these compositions do not contain sodium hydroxide or potassium hydroxide, many of them contain other ingredients which are environmentally undesirable particularly when used in concentration sufficient to provide effective oven cleaning.
Other methods of oven cleaning have been proposed, including the use of catalytic oven coatings intended to provide continuous self cleaning at normal baking temperatures; however, they tend to lose their effectiveness over time. Another method has been to design ovens for self cleaning with auxiliary heaters intended to raise oven temperatures to about 900.degree. C. in order to burn off the baked-on food residue. However, resorting to such high temperatures requires specially designed oven locks, additional insulation, etc., all of which renders this system generally undesirable for domestic use. Thus, as a practical matter, improved oven cleaning effectiveness will depend on the development of suitable and efficient detergent-type compositions.
Early efforts to develop non-caustic oven cleaners are represented, for example, by British Patent Specification No. 1,275,740, which discloses an aqueous composition comprising an amine component, which reacts with grease and fat at elevated temperatures to loosen cooking residue, and at least one anionic or non-ionic surfactant. A number of amines are disclosed and the preferred amine is monoethanolamine. The subject compositions also preferably contain an alkali-stable organic solvent. A wide variety of such solvents are disclosed including various glycols such as ethylene glycol and propylene glycol. The compositions preferably also contain an alkaline builder of which sodium carbonate appears to be preferred. The compositions are designed to be used in ovens pre-heated to a temperature of from about 65.degree. to about 120.degree. C.
U.S. Pat. No. 3,658,711 discloses a non-caustic water-based oven cleaning composition comprising a soap, an "inorganic cleaner", and an "amine enhancing agent". Included among the inorganic cleaners are sodium and potassium carbonates. Preferably, the compositions also include, as humectants, various organic solvents including diethylene glycol monobutyl ether. Although there is a statement to effect that the disclosed compositions can be applied at ambient room temperature, it is also stated quite clearly that the most efficient method of using the compositions is to apply them to an oven pre-heated and maintained at a temperature of about 93.degree. C.
U.S. Pat. No. 3,806,460 discloses oven cleaner compositions which can be used at temperatures as low as about 65.degree. C. The composition comprises alkali metal or ammonium salts of various inorganic acids, such as sodium or potassium carbonates, as a required "non-caustic inorganic cleaner". Another required ingredient is an amine or ammonia; among the possible amines, monoethanolamine and diethanolamine are mentioned, although these are not preferred. A third required ingredient appears to be an organic solvent having a boiling point above 120.degree. C. and these can include various ethers and alcohols.
U.S. Pat. Nos. 3,808,051, 3,881,948, 4,116,848, 4,193,886 and 4,236,935 constitute a series of patents disclosing non-caustic oven cleaners in which the operating temperatures are in the range of about 120.degree. C. to 287.degree. C. In U.S. Pat. Nos. 3,808,051 and 4,116,848, the compositions include at least one alkali metal salt of a weak organic acid. A possible additional ingredient in these compositions is a polyhydric alcohol, particularly sorbitol. In U.S. Pat. No. 3,881,948, the polyhydric alcohol (sorbitol) is the key ingredient and, in addition, an "alkaline acting catalyst" capable of accelerating alcoholysis reactions is required. The alkaline acting catalyst include various alkali metal and alkaline earth metal bases and salts, such as sodium carbonate and potassium carbonate, and even sodium or potassium hydroxide (in which case, the compositions cannot be regarded as non-caustic). U.S. Pat. Nos. 4,193,886 and 4,236,935 disclose weakly alkaline oven cleaning compositions comprising a polyhydric alcohol, at least one alkali metal salt of a weak organic acid, and an alkali metal bicarbonate to accelerate the alcoholysis reaction. Even though the title of U.S. Pat. No. 4,193,886 is "Novel Low Temperature Cleaner", the minimum operating temperature is 120.degree. C., with the preferred temperature being in the range of about 150.degree. to 175.degree. C.
U.S. Pat. No. 3,813,343 discloses oven cleaning compositions in which dimethylsulphoxide is added to facilitate removal of grease and fat.
U.S. Pat. No. 4,105,574 discloses a non-caustic oven cleaner comprising monoethanolamine, an etherified alkylene glycol solvent and, as a third essential ingredient, a specific sodium magnesium silicate thickening agent. The preferred etherified alkylene glycol solvent is diethylene glycol monoethyl ether, but diethylene glycol monobutyl ether is also mentioned. The disclosed composition can also contain "alkaline builders", with sodium and potassium carbonates mentioned. The operating temperature for oven cleaning is about 93.degree. C.
U.S. Pat. No. 4,135,947 discloses oven cleaning compositions which are usable at the relatively low temperature of 90.degree. C. The compositions require (1) a water soluble organic amine which can be monoethanolamine or diethanolamine, (2) a water soluble organic solvent which, in many specific examples, is diethylene glycol monobutyl ether (termed "2-butoxyethoxy-ethanol"), and (3) a sufficient amount of carbon dioxide to reduce the pH of the composition to a value of 10 or less.
Canadian Patent No. 1,047,903 discloses an oven cleaner operative at room temperature. The principal cleaning ingredient is an alkanolamine, but a "small amount"--0.5% to 4% --of an alkali metal hydroxide is also required.
The various non-caustic oven cleaner compositions currently available have been less than ideal: some require undesirably high operating temperatures; in some, cleaning effectiveness is not sufficient at concentrations which are not irritating to the user; some employ too high a concentration of volatile organic compounds and thus violate environmental regulations; etc. Accordingly, it would be desirable to provide a non-caustic aqueous based oven cleaner composition which does not have these disadvantages.